1. Field of the Invention
The invention relates to a wireless network communications, and more particularly to uplink/downlink transmission coordination between different cells to avoid inter-cell interference in wireless communications systems.
2. Description of the Related Art
Due to mobile communication technology advancements in recent years, various communications services, such as voice call services, data transfer services, and video call services, etc., may be provided to users regardless of their locations. Most mobile communications systems are multiple access systems in which access and wireless network resources are allocated to multiple users. The multiple access technologies employed by the mobile communications systems include the 1× Code Division Multiple Access 2000 (1×CDMA 2000) technology, the 1× Evolution-Data Optimized (1× EVDO) technology, the Orthogonal Frequency Division Multiplexing (OFDM) technology, and the Long Term Evolution (LTE) technology. Evolved from the LTE, the LTE Advanced is a major enhancement of the LTE standard. The LTE Advanced should be compatible with LTE equipment, and should share frequency bands with the LTE communications system. One of the important LTE Advanced benefits is its ability to take advantage of advanced topology networks, wherein optimized heterogeneous networks have a mix of macros with low power nodes such as picocells, femtocells and new relay nodes.
FIG. 1 shows an exemplary heterogeneous network (HetNet) deployment. Within the coverage area 100 of a macro evolved node B (eNB) 101, several low power nodes having smaller coverage areas are deployed so as to improve the overall system capacity. As shown in the figure, a pico eNB (also called a picocell) 102, a femto eNB (also called a femtocell) 103 and a relay eNB 104 are deployed with the coverage area 100 of the macro eNB 101. However, such HetNet deployment may cause undesired inter-cell interference. For example, suppose that the user equipment (UE) 202 camps on the pico eNB 102 as a serving cell. When the UE 202 moves to the cell edge of pico eNB 102, the signal transmitted by the macro eNB 101 adjacent to the UE 202 may become a strong interference to the UE 202 since the power of the signal transmitted by the pico eNB 102 may be weak when the signal reaching the UE 202. For another example, when a UE 201 not belong to the closed subscriber group (CSG) of the femto eNB 103 moves to the coverage area thereof, the signal transmitted by the femto eNB 103 may also become a strong interference to the UE 201. For yet another example, the signal transmitted by the macro eNB 101 may also be an interference to the UE 203 when the relay eNB 104 is transmitting signal or data to the UE 203 at the same time.
In order to solve the above-mentioned problems, methods and apparatus for uplink/downlink transmission coordination between different cells to avoid inter-cell interference in wireless Orthogonal Frequency Division Multiple Access (OFDMA) communications systems are provided.